1. Field of the Invention
The present invention relates to an apparatus and method to modulate address data and an apparatus and method to demodulate the address data therefor, and more particularly, to an apparatus and method to modulate address data, by which the address data of data to be recorded on a disc type recording medium is modulated into a wobble signal and a disc track is shaped in a form of the wobble signal, and an apparatus and method to demodulate the address data therefor.
2. Description of the Related Art
In a disc type recording medium, such as a compact disc (CD), address data is recorded on a header region that is separate from a disc track on which data is recorded.
Recently a new approach to record the address data has been introduced, which involves recording the address data by modulating the address data into a wobble signal and shaping the disc track in a form of the wobble signal. The address data can be modulated into the wobble signal by using monotone wobble (MW), saw tooth wobble (STW), binary phase shift keying (BPSK), or frequency shift keying (FSK). Theses approaches are advantageous with respect to a disc access such as a motor speed control.
FIG. 1 is a view illustrating a conventional disc track shaped in a form of the wobble signal and pits formed in the disc track. By using MW, the address data is modulated into the wobble signal in a form of a sine wave with a single frequency while the pits are formed in a middle of the disc track, resulting in the disc track being shaped in the form of the wobble signal. The pits corresponding to one address are grouped as a unit recording block. Respective lengths of the unit recording block and the disc track including a unit recording block change with an amount of the data to be recorded in the unit recording block. In general, a length of the wobble signal indicating one address is equal to that of one unit recording block. In addition, the address data is modulated into a unit wobble signal that includes a predetermined number of carrier signals. Each bit of address data or additional data is modulated into the predetermined number of carrier signals. For example, each bit of address data or additional data may be modulated into the unit wobble signal that includes 56 carrier signals.
According to recent specifications for high-density DVDs, 64 kbits of data are recorded based on the address the data indicated by the unit wobble signal. Thus, if one address is affected by a defect in a disk track, 64 kbits of data are inaccessible. In the case of high-density DVDs, capable of recording data in the tens of Gbits, the damage to the 64 kbits of data is not a big problem compared to a case of the disc with a small recording capacity. In order to solve such a problem, the amount of data recorded at one address may be reduced. In this case, a length of the unit recording block is reduced in accordance with a reduction in the amount of recorded data. However, the length of the unit wobble signal indicating one address does not change. Thus, discrepancy occurs between the length of address data indicated by the unit wobble signal and the length of data to be recorded at the address. Moreover, according to the conventional disc tract described above, because the unit wobble signal including predetermined number of carrier signals indicates one bit of address data, reducing the length of the wobble signal indicating one bit of address data to equalize the length of the wobble signal with a reduced length of the unit recording block does not make it possible to indicate one bit of address data with the unit wobble signal.